Polyhexamethylene Biguanide (PHMB): Uses & Dosage

Polyhexamethylene Biguanide (PHMB) is an anti-infective eye drop used to treat a severe eye infection called Acanthamoeba keratitis.

Drug class	Anti-amoebic
Type	Single
Forms	Eye Drop
Common strength	0.02% / 0.08%
Common Indian brands	Prepared in hospital pharmacy
Prescription status	Prescription (hospital-prepared)

What Polyhexamethylene Biguanide (PHMB) is used for

Polyhexamethylene Biguanide (PHMB) eye drops are a specialized medicine used to treat a very serious eye infection. This infection is:

Acanthamoeba keratitis: This is a severe infection of the cornea (the clear front part of your eye). It is often linked to improper contact lens use, such as washing or storing contact lenses with tap water, or using contaminated water.

Because Acanthamoeba keratitis is a serious condition, treatment with PHMB is carefully managed by eye specialists at Pristine Eye Hospitals.

How it works

Polyhexamethylene Biguanide (PHMB) works by targeting and disrupting the outer layer (membrane) of the Acanthamoeba organism. This action effectively kills both the active, moving forms of the amoeba and their tough, resistant cyst forms. By eliminating both forms, PHMB helps to clear the infection from your eye.

How it’s used

Polyhexamethylene Biguanide (PHMB) eye drops are prescribed by your ophthalmologist at Pristine Eye Hospitals and are prepared specially for you in the hospital pharmacy. It is crucial to follow your doctor’s instructions precisely for its use.

Typically, treatment for Acanthamoeba keratitis with PHMB eye drops begins with very frequent application, often hourly, day and night. This intensive initial phase is vital to combat the infection effectively. As your eye begins to heal and the infection comes under control, your doctor will slowly reduce the frequency of the drops over several months. It is very important not to stop using the drops or change the dosing schedule without consulting your ophthalmologist, even if your eye feels better. The treatment duration is long, often lasting many months, to ensure the infection is completely eradicated and to prevent it from returning.

Your doctor will guide you on the exact strength (either 0.02% or 0.08%) and the specific tapering schedule that is right for your condition. Always ensure your hands are clean before applying the drops, and avoid touching the tip of the dropper to your eye or any other surface to prevent contamination.

Always follow your ophthalmologist’s exact instructions.

Brands available in India

Prepared in hospital pharmacy

Brand availability and pricing vary; confirm with your pharmacist.

Good to know

Prescription eye medicine — use only as directed by a qualified ophthalmologist. This page is for general education and is not a substitute for professional medical advice, diagnosis or a prescription. Do not self-medicate or reuse an old prescription. This is given only by specialists in a hospital or clinic setting and is never for self-use.

Precautions & side effects

When using Polyhexamethylene Biguanide (PHMB) eye drops, it is very important to be aware of certain precautions to ensure the best possible outcome for your treatment and to prevent recurrence of the infection:

Long Treatment Duration: Treatment for Acanthamoeba keratitis with PHMB lasts many months. It is crucial to continue using the drops exactly as prescribed by your ophthalmologist for the entire duration, even if your symptoms improve. Stopping treatment early can lead to the infection returning.
Contact Lens Hygiene: If you wear contact lenses, it is absolutely critical to understand that improper contact lens hygiene is the main risk factor for Acanthamoeba keratitis. Never wash or store your contact lenses with tap water. Tap water, even if it seems clean, can contain Acanthamoeba and other microorganisms. Always use only sterile contact lens solutions recommended by your eye care professional.
Prescription Medicine: PHMB is a prescription eye medicine. Use it only as directed by a qualified ophthalmologist. This page provides general education and is not a substitute for professional medical advice, diagnosis, or a prescription. Do not self-medicate or reuse an old prescription. This medicine is given only by specialists in a hospital or clinic setting and is never for self-use.
Follow Doctor’s Instructions: Adhere strictly to the dosing schedule and any other instructions given by your doctor. If you miss a dose, contact your doctor for advice. Do not double dose.
Storage: Store the eye drops as advised by your hospital pharmacy, usually in a cool, dry place away from direct sunlight.
Contamination: Avoid touching the tip of the dropper to your eye, eyelid, or any other surface to prevent contamination of the medicine.
Consult Your Doctor: If you experience any new or worsening symptoms, or if you have any concerns about your treatment, contact your ophthalmologist immediately.

Understanding Acanthamoeba Keratitis

Acanthamoeba keratitis is a serious and potentially sight-threatening infection of the cornea, which is the clear, dome-shaped front surface of your eye. The cornea plays a vital role in focusing light onto the retina, allowing you to see clearly. When it gets infected, it can cause significant pain, redness, blurred vision, and sensitivity to light. If left untreated, or treated improperly, it can lead to permanent vision loss or even require a corneal transplant.

This infection is caused by a microscopic organism called Acanthamoeba, which is commonly found in water sources like tap water, swimming pools, hot tubs, and even soil. While anyone can potentially get this infection, it is most frequently associated with contact lens wearers. The main risk factors include:

Washing or rinsing contact lenses with tap water.
Storing contact lenses in non-sterile solutions or tap water.
Swimming, showering, or using a hot tub while wearing contact lenses.
Poor contact lens hygiene, such as not cleaning contact lens cases regularly or extending the recommended wear time for lenses.

At Pristine Eye Hospitals, our specialists are highly experienced in diagnosing and treating Acanthamoeba keratitis. Early diagnosis and diligent treatment, often involving medicines like Polyhexamethylene Biguanide (PHMB), are crucial for preserving your vision.

How to Correctly Use Eye Drops

Using eye drops correctly is essential for the medicine to work effectively and to prevent contamination. Here’s a step-by-step guide:

Wash Your Hands: Always start by thoroughly washing your hands with soap and water and drying them with a clean towel. This is the most important step to prevent introducing germs into your eye.
Prepare the Bottle: Gently shake the bottle if instructed by your doctor or pharmacist. Make sure the dropper tip is clean and not damaged. Do not let the tip touch any surface.
Position Yourself: Tilt your head back or lie down. Gently pull down your lower eyelid with one finger to create a small pocket.
Instil the Drop: Hold the dropper bottle above your eye, looking upwards. Squeeze the bottle gently to release one drop into the pocket you created. Try not to blink immediately.
Close Your Eye: Gently close your eye for a minute or two. Avoid squeezing your eyes shut tightly, as this can push the medicine out. You can also press lightly on the inner corner of your eye (near your nose) to help the medicine stay in your eye and reduce absorption into your bloodstream.
Clean Up: If any excess medicine runs down your face, gently wipe it away with a clean tissue.
Repeat if Necessary: If you need to instil more than one drop in the same eye, wait at least 5-10 minutes between drops to allow the first drop to be absorbed. If you are using different types of eye drops, wait at least 10-15 minutes between each type.
Wash Hands Again: Wash your hands again after applying the drops to remove any residual medicine.

Remember, never share your eye drops with anyone else, and always check the expiry date on the bottle. If you have any difficulty instilling the drops, ask your doctor or a family member for assistance.

General Eye Hygiene and When to Seek Help

Maintaining good eye hygiene is vital for overall eye health, especially when dealing with an eye infection. Always use clean hands when touching your eyes or applying medication. If you wear contact lenses, strictly follow all hygiene guidelines provided by your eye care professional, particularly regarding cleaning, disinfection, and storage. Never use tap water for your contact lenses, and always use fresh, sterile solution. Replace your contact lens case regularly, typically every 1-3 months, as cases can harbour bacteria and other microorganisms.

It is important to be vigilant about your eye health and know when to seek professional medical help. While using PHMB eye drops for Acanthamoeba keratitis, your doctor will schedule regular follow-up appointments to monitor your progress. However, you should contact Pristine Eye Hospitals immediately if you experience any of the following:

Sudden worsening of eye pain, redness, or discomfort.
Significant decrease in vision.
Increased sensitivity to light.
New or unusual discharge from your eye.
Any allergic reaction, such as severe itching, swelling, or difficulty breathing (though rare with eye drops).
If you accidentally run out of your medicine or miss several doses.

Your ophthalmologist is your best resource for managing your eye condition. Do not hesitate to reach out with any concerns or questions. Early intervention and consistent communication with your care team are key to a successful recovery.

Frequently asked questions

What is Polyhexamethylene Biguanide (PHMB) used for?

Polyhexamethylene Biguanide (PHMB) eye drops are used to treat a severe eye infection called Acanthamoeba keratitis, which affects the cornea (the clear front part of the eye).

How does Polyhexamethylene Biguanide (PHMB) work?

PHMB works by disrupting the outer layer (membrane) of the Acanthamoeba organism, effectively killing both the active and cyst forms of the amoeba to clear the infection.

What are the common Indian brands of Polyhexamethylene Biguanide (PHMB)?

Polyhexamethylene Biguanide (PHMB) eye drops are typically prepared in the hospital pharmacy and are not available under specific commercial brand names for purchase outside of a hospital or clinic setting.

How is Polyhexamethylene Biguanide (PHMB) used?

PHMB eye drops are usually started hourly day and night, and then the frequency is slowly reduced over many months as directed by your ophthalmologist. The treatment duration is long.

Is a prescription needed for Polyhexamethylene Biguanide (PHMB)?

Yes, Polyhexamethylene Biguanide (PHMB) is a prescription medicine and must only be used under the direct supervision and prescription of a qualified ophthalmologist. It is prepared in a hospital pharmacy and is not for self-use.

What are the key precautions to take when using Polyhexamethylene Biguanide (PHMB)?

The treatment lasts many months, so it's crucial to follow the doctor's instructions precisely. A major precaution, especially for contact lens wearers, is to never wash or store contact lenses with tap water, as this is the main risk factor for the infection PHMB treats.

References

Medically reviewed by Dr. C Jagadesh Reddy, Chief Surgeon: Cornea, Cataract and Refractive Surgery — last reviewed 2026-07-28.

This page is for general education only and is not a substitute for professional medical advice, diagnosis or treatment. Never self-medicate or reuse an old prescription. Always consult a qualified ophthalmologist before starting, changing or stopping any eye medicine.